﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace PayloadTracker.APRS.SoundModem
{
    public delegate void AX25PacketReadyDelegate(AX25Packet packet);
    public class AX25Deserializer
    {
        public enum CONSTS : byte
        {
            SEPARATOR = 0x7E // 0111110
        }
        byte m_BitAcc, m_ByteAcc;
        int m_ByteAccLen;
        int m_TrueBitsInaRow;
        List<Byte> m_BytesToProcess;

        public event AX25PacketReadyDelegate AX25PacketReady;

        //construcotr
        public AX25Deserializer()
        {
            m_BytesToProcess = new List<byte>();
            m_BitAcc = m_ByteAcc = 0;
            m_TrueBitsInaRow = m_ByteAccLen = 0;
        }
        //reset function
        private void Reset()
        {
            m_BytesToProcess.Clear();
            m_BitAcc = 0;
            m_ByteAcc = 0;
            m_ByteAccLen = 0;
        }
        static int cnt = 0;
        
        public void ProcessBit(bool bit)
        {//called from the FSK when a bit is ready.


            //Logger.LOG.Write(bit ? "1" : "0");

            if (m_TrueBitsInaRow == 5 && !bit)
            {
                //bit packing get out.
                m_TrueBitsInaRow = 0;
                return;
            }
            if (bit)
                m_TrueBitsInaRow++;
            else
                m_TrueBitsInaRow = 0;



            m_BitAcc = ((byte)(((uint)m_BitAcc) << 1));
            if (bit) m_BitAcc |= 1;


            if (m_BitAcc == ((Byte)CONSTS.SEPARATOR))
            { 
                //                if (b == (Byte)CONSTS.SEPARATOR)

                Logger.LOG.WriteLine("Got AX.25 FLAG " + ++cnt);
                //We have one of of our lovely flag bytes.
                if (m_BytesToProcess.Count > 1)
                {//if we already have a packet going put it through and assemble.
                    ProcessByte(((Byte)CONSTS.SEPARATOR));
                    Reset();
                    ProcessByte(((Byte)CONSTS.SEPARATOR));
                }
                else if (m_BytesToProcess.Count == 1)
                {
                    //We already have just 1 so the one in the queue is now bunk.
                    //get rid of the cue this one.
                    Reset();
                    ProcessByte(((Byte)CONSTS.SEPARATOR));
                }
                else if (m_BytesToProcess.Count == 0)
                {
                    //this is obviously the first one.
                    m_ByteAccLen = 0;
                    ProcessByte(((Byte)CONSTS.SEPARATOR));
                    m_ByteAcc = 0;

                }

            }
            else if (m_BytesToProcess.Count > 0)
                //we have something going so lets keep it up!
                AssembleByte(bit);

        }
        public void AssembleByte(bool bit)
        {
            //Most significant bit first.
            //m_ByteAcc = ((byte)(((uint)m_ByteAcc) << 1));
            //if (bit) m_ByteAcc |= 1;

            //Least significant bit first.
            if (bit) m_ByteAcc = ((byte)(((int)m_ByteAcc) | (1 << m_ByteAccLen)));

            if (++m_ByteAccLen == 8)
            {
                //we have assembled a byte!
                m_ByteAccLen = 0;
                ProcessByte(m_ByteAcc);
                m_ByteAcc = 0;
            }
        }
        private void ProcessByte(Byte b)
        {


            //string bitstring = Convert.ToString(b, 2);
            //while (bitstring.Length < 8)
            //    bitstring = "0" + bitstring;
            //Logger.LOG.WriteLine("Byte received: " + bitstring);

            m_BytesToProcess.Add(b);

            if (b == (Byte)CONSTS.SEPARATOR && m_BytesToProcess.Count > 2)
            {
                //add the end byte and assemble it and reset for next frame.
                AssembleFrame();
                Logger.LOG.WriteLine("Finished assembling frame. Resettings.");
            }
        }

        private void AssembleFrame()
        {
            Logger.LOG.WriteLine("Assembling Frame... ");

            try
            {


                foreach (byte b in m_BytesToProcess)
                {
                    string bitstring = Convert.ToString(b, 2);
                    while (bitstring.Length < 8)
                        bitstring = "0" + bitstring;

                    Logger.LOG.WriteLine("Byte: " + bitstring + " H: 0x" + Convert.ToString(b, 16) + " D: " + b.ToString() + " A: " + System.Text.ASCIIEncoding.ASCII.GetString(new byte[] { b }));

                }

                //do checksum check.
                ushort computedcrc = (ushort)crc_ccitt();

                

                byte[] bcrc = m_BytesToProcess.GetRange(m_BytesToProcess.Count - 3, 2).ToArray();
                ushort crc = ((ushort)((((uint)bcrc[1]) << 8) | ((uint)bcrc[0])));

                System.Diagnostics.Debug.WriteLine("DS CRC: " + crc);

                if (computedcrc != crc)
                //if(!CheckCRC_CCITT())
                {
                    Logger.LOG.Error("Invalid AX.25 Packet CRC, discarding... (probably too much noise or incorrect volume) " + computedcrc + " vs " + crc);
                    return;
                }



                int o = 1;

                //get the callsigns & ssids.
                string callsign1 = string.Empty;
                for (int i = 1; i <= 6; i++)
                {
                    byte ascii = ((byte)(m_BytesToProcess[i] >> 1));
                    callsign1 += System.Text.ASCIIEncoding.ASCII.GetString(new byte[] { ascii });
                }
                byte callsign1ssid = ((byte)((m_BytesToProcess[7] >> 1) & 0x3F));

                string callsign2 = string.Empty;
                for (int i = 8; i <= 13; i++)
                {
                    byte ascii = ((byte)((m_BytesToProcess[i] >> 1)));
                    callsign2 += System.Text.ASCIIEncoding.ASCII.GetString(new byte[] { ascii });
                }
                byte callsign2ssid = ((byte)((m_BytesToProcess[14] >> 1) & 0x3F));

                //Logger.LOG.WriteLine("Callsign1: " + callsign1 + " (" + callsign1ssid + ")");
                //Logger.LOG.WriteLine("Callsign2: " + callsign2 + " (SSID:" + callsign2ssid + ")");

                o = 13;
                //trim the rest of the address field possibly do something with it?
                while ((m_BytesToProcess[o++] & 1) != 1) ;

                byte control = m_BytesToProcess[o++];

                if ((control & 3) != 3)
                {//we ONLY care about U Frames not S frames or I frames.
                    Logger.LOG.WriteLine("AX.25 Frame with Control of " + Convert.ToString(control, 2) + " received. Ignoring frame! (We wanted 00000011)");
                    return;
                }

                byte pid = m_BytesToProcess[o++];

                byte[] data = m_BytesToProcess.GetRange(o, m_BytesToProcess.Count - 3 - o).ToArray();


                //build and fire event.
                AX25Packet packet = new AX25Packet();
                packet.CallsignFrom = callsign1;
                packet.SSIDFrom = System.Text.ASCIIEncoding.ASCII.GetString(new byte[] { callsign1ssid });
                packet.CallsignTo = callsign2;
                packet.SSIDTo = System.Text.ASCIIEncoding.ASCII.GetString(new byte[] { callsign2ssid });
                packet.PID = pid;
                packet.Control = control;

                packet.Data = data;

                AX25PacketReadyDelegate handler = AX25PacketReady;
                if (handler != null)
                    handler(packet);
            }

            catch (System.Exception e)
            {
                Logger.LOG.Error("Failed to deserialize AX.25 frame due to: " + e.ToString());
                Reset();
            }
        }


        static readonly ushort[] crc_ccitt_table = {
        0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
        0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
        0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
        0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
        0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
        0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
        0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
        0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
        0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
        0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
        0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
        0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
        0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
        0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
        0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
        0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
        0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
        0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
        0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
        0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
        0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
        0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
        0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,
        0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
        0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,
        0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
        0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
        0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
        0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
        0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
        0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
        0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
};

        //compute checksum.
        private ushort crc_ccitt()
        {
            ushort crc = 0xffff;
            for (int i = 1; i < m_BytesToProcess.Count - 3; i++)
                crc = crc_ccitt_byte(crc, m_BytesToProcess[i]);
            return (ushort)~crc;
        }
        //table lookup.
        static ushort crc_ccitt_byte(ushort crc, byte c)
        {
            return (ushort)((crc >> 8) ^ crc_ccitt_table[(crc ^ c) & 0xff]);
        }
    }
}
